Towards a circular economy: A novel microalgal two-step growth approach to treat excess nutrients from digestate and to produce biomass for animal feed
Volume 320, Part A,
Link to the paper
Abstract: Implementing a circular economy aimed at reusing resources is becoming increasingly important for industry. Microalgae fit within a circular economy by being able to bioremediate nutrient waste and as a source of biomass for several commercial applications. Here, we report a novel validation of a circular economy concept using microalgae at a relevant industrial scale with a new two-phase process. During the first phase, biomass was grown autotrophically, biomass was then concentrated using membrane technology for the second phase where mixotrophic conditions were applied to boost growth further. Microalgae cultures were able to grow (13.8 g/L), uptake and bioremediate nutrients (Nitrogen > 134 mg/L/day) from an anaerobic digestion side-stream (digestate), obtaining high-quality microalgae biomass (>45% protein content) suitable for use as animal feed, closing the circular economy loop for industrial applications.
Keywords: Circular economy; Microalgae; Digestate; Membrane filtration
Rahul Vijay Kapoore, Eleanor E. Wood, Carole A. Llewellyn,
Algae biostimulants: A critical look at microalgal biostimulants for sustainable agricultural practices,
Abstract: For the growing human population to be sustained during present climatic changes, enhanced quality and quantity of crops are essential to enable food security worldwide. The current consensus is that we need to make a transition from a petroleum-based to a bio-based economy via the development of a sustainable circular economy and biorefinery approaches. Both macroalgae (seaweeds) and microalgae have been long considered a rich source of plant biostimulants with an attractive business opportunity in agronomy and agro-industries. To date, macroalgae biostimulants have been well explored. In contrast, microalgal biostimulants whilst known to have positive effects on development, growth and yields of crops, their commercial implementation is constrained by lack of research and cost of production. The present review highlights the current knowledge on potential biostimulatory compounds, key sources and their quantitative information from algae. Specifically, we provide an overview on the prospects of microalgal biostimulants to advance crop production and quality. Key aspects such as specific biostimulant effects caused by extracts of microalgae, feasibility and potential of co-cultures and later co-application with other biostimulants/biofertilizers are highlighted. An overview of the current knowledge, recent advances and achievements on extraction techniques, application type, application timing, current market and regulatory aspects are also discussed. Moreover, aspects involved in circular economy and biorefinery approaches are also covered, such as: integration of waste resources and implementation of high-throughput phenotyping and -omics tools in isolating novel strains, exploring synergistic interactions and illustrating the underlying mode of microalgal biostimulant action. Overall, this review highlights the current and future potential of microalgal biostimulants, algal biochemical components behind these traits and finally bottlenecks and prospects involved in the successful commercialisation of microalgal biostimulants for sustainable agricultural practices.
Keywords: Algae biostimulants; Sustainable agriculture; Microalgae biotechnology; Metabolomics; Consortia; Biorefinery; Circular economy; Bioremediation
Fleuriane Fernandes, Alla Silkina, Claudio Fuentes-Grünewald, Eleanor E. Wood, Vanessa L.S. Ndovela, Darren L. Oatley-Radcliffe, Robert W. Lovitt, Carole A. Llewellyn,
Valorising nutrient-rich digestate: Dilution, settlement and membrane filtration processing for optimisation as a waste-based media for microalgal cultivation,
Abstract: Digestate produced from the anaerobic digestion of food and farm waste is primarily returned to land as a biofertiliser for crops, with its potential to generate value through alternative processing methods at present under explored. In this work, valorisation of a digestate resulting from the treatment of kitchen and food waste was investigated, using dilution, settlement and membrane processing technology. Processed digestate was subsequently tested as a nutrient source for the cultivation of Chlorella vulgaris, up to pilot-scale (800L). Dilution of digestate down to 2.5% increased settlement rate and induced release of valuable compounds for fertiliser usage such as nitrogen and phosphorus. Settlement, as a partial processing of digestate offered a physical separation of liquid and solid fractions at a low cost. Membrane filtration demonstrated efficient segregation of nutrients, with micro-filtration recovering 92.38% of phosphorus and the combination of micro-filtration, ultra-filtration, and nano-filtration recovering a total of 94.35% of nitrogen from digestate. Nano-filtered and micro-filtered digestates at low concentrations were suitable substrates to support growth of Chlorella vulgaris. At pilot-scale, the microalgae grew successfully for 28 days with a maximum growth rate of 0.62 day−1 and dry weight of 0.86 g⋅L−1. Decline in culture growth beyond 28 days was presumably linked to ammonium and heavy metal accumulation in the cultivation medium. Processed digestate provided a suitable nutrient source for successful microalgal cultivation at pilot-scale, evidencing potential to convert excess nutrients into biomass, generating value from excess digestate and providing additional markets to the anaerobic digestion sector.
Keywords: Digestate; Membrane filtration; Settlement and dilution; Microalgae; Chlorella vulgaris; Pilot-scale
Carole A. Llewellyn, Rahul Vijay Kapoore, Robert W. Lovitt, Carolyn Greig, Claudio Fuentes-Grünewald, Bethan Kultschar
Llewellyn C.A., Kapoore R.V., Lovitt R.W., Greig C., Fuentes-Grünewald C., Kultschar B. (2019) Deriving Economic Value from Metabolites in Cyanobacteria. In: Hallmann A., Rampelotto P. (eds) Grand Challenges in Algae Biotechnology. Grand Challenges in Biology and Biotechnology. Springer, Cham. https://doi.org/10.1007/978-3-030-25233-5_15
Part of the Grand Challenges in Biology and Biotechnology book series (GCBB)
Abstract: This chapter focuses on the challenges associated with achieving economic value from metabolites derived from cyanobacteria. Significant advances have been made in cyanobacterial biotechnology in the last few years. However, the field is still immature, and many challenges remain. We start with a critical overview of the main technologies associated with cultivation, cell disruption and metabolite extraction. Then, we provide an overview of current significant metabolite groups from cyanobacteria relevant to industry covering phycobilins, carotenoids, polysaccharides, peptides, lipids, mycosporine-like amino acids, polyhydroxyalkanoates, cyanotoxins and platform chemicals, and the potential for stable isotopes production. We cover metabolites that are already in the market and those with future potential with a focus on spirulina (Arthrospira) the most commercially developed species of cyanobacteria. As large-scale cultivation and downstream processing techniques continue to develop further, combining this with a systems biology and biorefinery approach will ensure that the best economic and environmental sustainability value can be achieved.